How long is a typical horse race?

The length is about 440 yards. Different race lengths can be established by locating the starting box at various points on the track. At Derby Lane the 5/16th (1,650 feet) and the 3/8th (1,980 feet) distances are run. Other distances offered around the country are 1/4 mile and 7/16th mile distances.

Except from http://www.derbylane.com/history_faq.asp